It is estimated that approximately 50 million people in the US have high blood pressure. The criteria for diagnosis of hypertension has changed: a blood pressure of 120/80 mm Hg is considered normal; 120-139 or 80-89 mmHg is defined as pre-hypertensive; greater than or equal to 140-159 mm Hg systolic or 90-99 mm Hg diastolic is stage I hypertension; and greater than or equal to 160 mm Hg systolic or greater than or equal to 100 mm Hg diastolic is stage II hypertension. (The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure, (JNC 7), NHLBI publication, Hypertension 42:1206, 2003). Of those who have been diagnosed, about two thirds do not achieve blood pressure control of less than 140/90 mm Hg, and nearly 15% receive no treatment at all. About half of the people with hypertension never know they have high blood pressure because of the lack of specific symptoms. In most cases of hypertension, the cause is unknown, so the diagnosis is called primary hypertension. In about 5 to 10 percent of people, high blood pressure is a secondary symptom of some other medical condition. For example, there might be an organic cause such as kidney disease, tumor of the adrenal glands, heart defects, or disorders of the nervous system.
Aggressive drug treatment of long-term high blood pressure can significantly reduce the incidence of death from heart disease and other causes in both men and women. In people with diabetes, controlling both blood pressure and blood glucose levels prevents serious complications of that disease. If patients have mild hypertension and no heart problems, then lifestyle changes may suffice to control the condition. For more severe hypertension or for mild cases that do not respond to changes in diet and lifestyle within a year, drug treatment is usually necessary. A single-drug regimen is usual to control mild to moderate hypertension. More severe hypertension often requires a combination of two or more drugs. Prolonged-release drugs are being developed so that they are most effective during early morning periods, when patients are at highest risk for heart attack or stroke.
It is very important to rigorously maintain a drug regimen. Patients who discontinue antihypertensive therapy, particularly smokers and younger adults, are at a significantly increased risk for stroke. All drugs used for hypertension have side effects. Common side effects include fatigue, coughing, skin rash, sexual dysfunction, depression, cardiac dysfunction, or electrolyte abnormalities. Because of these side effects finding the best drug for the patient while encouraging ongoing patient compliance may be difficult.
Congestive heart failure (CHF) is a condition where the heart pump efficiency (cardiac output) of the heart becomes so low that blood circulation is inadequate to meet tissue needs. Congestive heart failure is usually a progressively worsening condition resulting in serious disability and death. Approximately five million Americans, with a significant percentage being under the age of 60 years, suffer from CHF. Past research suggests that a slowing an elevated heart rate can improve heart performance.
Despite the availability of many therapies, hypertension and congestive heart failure remain major health issues. Many of the therapies have undesirable side effects, or do not achieve adequate control of blood pressure or heart rate. Thus, there remains a need to develop systems and methods for regulating blood pressure and/or heart rate.